EXPR =
  '<expr>' [ DEFUN | DEFMACRO | DEFVAR | TERM ] * '</expr>'

TERM = [ VAR | DIRECT | FUNCALL ]

TYPE = 'integer' | 'string' | 'boolean' | 'symbol' | 'list'

DEFUN =
  '<defun fname="' FUNCNAME '">'
  ARGS ?
  TERM *
  '</defun>'

ARGS =
  '<args>' [ SYMBOL | VAR ] * OPTIONAL ? REST ? '</args>'

OPTIONAL =
  '<optional/>' [ SYMBOL | VAR ] *

REST =
  '<rest/>' [ SYMBOL | VAR ]

DEFVAR = DEFVAR-INT DEFVAR-STR DEFVAR-BOOL

DEFVAR-INT =
  '<defvar vname="' VARNAME '">'
  DESCRIPTION ?
  INT ?
  <possible-value>[ INT | '<range>' INT INT '</range>' ] *</possible-value>
  '</defvar>'

DEFVAR-STR =
  '<defvar vname"' VARNAME '">'
  DESCRIPTION ?
  STR ?
  <possible-value> STR * </possible-value>
  '</defvar>'

DEFVAR-BOOL =
  '<defvar vname"' VARNAME '">'
  DESCRIPTION ?
  BOOL ?
  '</defvar>'

DESCRIPTION =
  '<description>' TEXT '</description>'

VAR =
  '<variable vname="' NAME '"/>'

DIRECT = INT STR BOOL SYMBOL LIST

INT =
  '<const type="integer">' INTEGER '</const>'
STR =
  '<const type="string">' STRING '</const>'
BOOL =
  '<const type="boolean">' [ 'true' | 'false' ] </const>
SYMBOL =
  '<const type="symbol">' NAME '</const>'
LIST =
  '<const type="list">' DIRECT * '</const>' | <const type="list"/>

FUNCALL =
  '<funcall fname="' PREDEFINED-FUNC-NAME '">' TERM * '</funcall>'
  | '<' PREDEFINED-FUNC-SYMBOL '>' TERM * '</' PREDEFINED-FUNC-SYMBOL '>'
  | '<' PREDEFINED-MACRO-SYMBOL '>' TERM * '</' PREDEFINED-MACRO-SYMBOL '>'

PREDEFINED-FUNC-SYMBOL =
  'set'
  | 'and' | 'or' | 'not'
  | 'lt' | 'le' | 'eq' | 'ge' | 'gt'
  | 'noteq'
  | 'add' | 'sub' | 'mul' | 'div' | 'mod'
  | 'add-set' | 'sub-set' | 'mul-set' | 'div-set' | 'mod-set'
  | 'logand' | 'logior' | 'logxor' | 'lsh'
  | 'logand-set' | 'logior-set' | 'logxor-set' | 'lsh-set'
  | 'append' | 'concat' | 'substr'
  | 'cons' | 'car' | 'cdr' | 'nth'

PREDEFINED-FUNC-NAME =
  PREDEFINED-FUNC-SYMBOL
  | '='
  | '&&' | '||' | '!'
  | '<' | '<=' | '==' | '>=' | '>'
  | '!='
  | '+' | '-' | '*' | '/' | '%'
  | '+=' | '-=' | '*=' | '/=' | '%='
  | '&=' | '|=' | '~=' | '<<=' | '>>='

PREDEFINED-MACRO-SYMBOL =
  'case' | 'cond' | 'if' | 'progn' | 'when' | 'while'

PREDEFINED-MACRO-NAME = PREDEFINED-MACRO-SYMBOL